Two-stroke and four stroke medium speed diesel engines such as those manufactured by Electromotive Diesels (EMD) of LaGrange, Ill. (formerly a division of General Motors) are used in locomotives, in power generating systems, and in marine propulsion applications. An example of one common type of diesel engine, depicted in FIG. 1, is an EMD 645 E-16 two-stroke, “roots-blown” engine having an exhaust system which comprises an elongated overhead exhaust manifold 4 which runs horizontally above the centerline of the engine 2. The overhead manifold 4 receives exhaust gas via a series of pairs of opposing manifold legs 6 which extend upwardly to the bottom of the horizontal exhaust manifold 4 from the individual cylinder exhaust ports of the engine 2. The exhaust from the vertical manifold legs 6 collects in the horizontal exhaust manifold 4 and flows out of the exhaust manifold 4 via one or more (typically a plurality of) exhaust stacks 3.
As is also known in the art, another common type of diesel engine is a turbocharged engine which is similar to the roots-blown engine 2 depicted in FIG. 1 except that the exhaust collected in the horizontal overhead exhaust manifold of the turbocharged engine flows from one of the longitudinal ends of the horizontal overhead exhaust manifold to a turbocharger.
Turbocharged and roots-blown diesel engines typically have either 8, 12 or 16 cylinders arranged in a V configuration. Consequently, the manifold legs 6 of the exhaust system extend upwardly from the cylinder ports to the overhead exhaust manifold 4 in a series of four, six or eight opposing pairs. The overhead exhaust manifold 4 is typically formed of a series of manifold sections 10 such that two opposing pairs of the manifold legs 6 are connected to each manifold section 10. Each manifold section 10 also typically includes a flange 12 on one or both of the longitudinal ends thereof for bolting to flanged expansion joints positioned between the other manifold sections 10.
A need presently exists for an effective catalytic converter system for treating the exhaust gas from diesel engines. The application of catalytic converter devices to the exhaust systems of two-stroke and four-stroke diesel engines has been difficult for several reasons. In many cases, particularly in locomotive applications, there is not sufficient space around the engine for installation of a catalytic converter system. In addition, the temperature of the exhaust from two-stoke and four-stroke engines is relatively low in terms of the temperature necessary to “light-off” the catalyst to initiate and maintain the conversion reaction. Further, these engines have a relatively high lube oil consumption rate. In addition, it is difficult in locomotive and other applications to remove the exhaust manifolds from the engines due to a lack of sufficient overhead space for the lifting equipment. Also, the back pressure limits of the turbocharged diesel engines are typically very low.